Acquired immunodeficiency syndrome (AIDS) is a disease resulting from human immunodeficiency virus (HIV) infection. The progression from the initial HIV infection to AIDS-related complex (ARC), AIDS, and AIDS with secondary-infections, which is the end stage of the disease, is long, variable in time and not completely understood (Weiss, R. A., How does HIV cause AIDS? Science 260:1273-1279 [1993]). Another recent review of HIV infection, the course that follows and the pathogenic mechanisms responsible for the clinical outcome is useful for up to date background purposes (Pantaleo, G., Graziosi, C. and Fauci, A. S. The immunopathogenesis of human immunodeficiency virus infection. New England Journal of Medicine 328:327-335 [19993]). A recently published broadly-encompassing article lists all the currently approved anti-HIV agents as well as drugs for the treatment of AIDS and its associated illnesses and secondary infections (Johnson, M. I. and Hoth, D. F., Present status and future prospects for HIV therapies. Science 260:1286-1293 [1993]). This article contains a broad outline of “Current State-of-the-Art Treatment”, “Therapies in Development” and “The Future of HIV Therapeutics.” An accompanying article of interest dealing with HIV therapeutic (rather than prophylactic) vaccine development is Haynes, B. F. Scientific and social issues of human immunodeficiency virus vaccine development. Science 260:1279-1286 [1993].
All the therapies which were developed or suggested for this disease up to now possess a narrow target, namely, they address a single aspect of the disease. The acknowledged therapies for HIV disease/AIDS are antiretroviral agents such as those approved (AZT or zidovudine, ddI or didanosine and DDC or zalcitabine) along with other antiretroviral agents which are now in clinical trials. The antiretroviral agents are divided into the following categories: reverse transcriptase inhibitors, protease inhibitors, Tat inhibitors, drugs that block viral entry into cells, and nucleic acid-based therapies. The other therapies currently in development are aimed at improving the immune system (“Immune Reconstitution”) thus enabling the human host to control HIV infection and its progression. Another general approach to the treatment of AIDS is the development of therapeutic HIV vaccines whereby HIV-infected individuals are treated with viral immunogens designed to boost the anti-HIV immune response and eradicate viral particles along with decreasing the number of virus-infected cells.
U.S. Pat. No. 4,880,918 entitled “Arrest and Killing of Tumor Cells by Adenosine 5′-Diphosphate and Adenosine 5′-Triphosphate” to Rapaport, U.S. Pat. No. 5,049,372 entitled “Anticancer Activities in a Host by Increasing Blood and Plasma Adenosine 5′-Triphosphate (ATP) Levels” to Rapaport, and U.S. Pat. No. 5,227,371 entitled “Utilization of Adenine Nucleotides and/or Adenosine and Inorganic Phosphate for Elevation of Liver, Blood and Blood Plasma Adenosine 5′-Triphosphate Concentrations” to Rapaport, disclose the treatment of cancer by administration of adenine nucleotides to a human host and/or disclose a method to expand organ, blood and blood plasma ATP pools by administration of adenine nucleotides and/or adenosine and inorganic phosphate to a human host.
The role of intracellular ATP as a cellular energy source, a phosphate group donor for phosphorylation reactions and an allosteric regulator of the activities of a variety of cellular proteins has been well-established. Only in the past 10 years have the roles of adenosine and ATP began to emerge as powerful physiological extracellular modulators of intravascular, extravascular and CNS functions, a role which is attracting significant attention within the field of drug development (Williams, M. Purinergic drugs: opportunities in the 1990's. Drug Development Research 28:438-444 [1993]). Adenosine is the endogenous ligand for the A (or P1) type purine receptors affecting mostly cardiovascular and CNS functions, whereas ATP is the ligand for P2 type purine receptors and is now an accepted neurotransmitter (Benham, C. D. ATP joins the fast lane. Nature 359:103-104 [1992]; Edwards, F. A., Gibb, A. J. and Colquhoun, D. ATP receptor-mediated synaptic currents in the central nervous system. Nature 359:144-147 [1992]).
The administration of adenine nucleotides (e.g., ATP, AMP or other adenine nucleotides) into the systemic circulation results in the immediate degradation of the nucleotide to adenosine and inorganic phosphate. This degradation in the vascular bed is followed by incorporation of the adenosine and inorganic phosphate into liver ATP pools (steady state levels) yielding significant expansion of the liver ATP pools, which is followed by an expansion of red blood cell ATP pools. The red blood cells with expanded ATP pools which are produced by this mechanism slowly release micromolar levels of ATP into the blood plasma without undergoing hemolysis, thus achieving elevated steady state extracellular ATP levels, in spite of the catabolic enzymatic activities present intravascularly (Rapaport, E. and Fontaine, J. Anticancer activities of adenine nucleotides in mice are mediated through expansion of erythrocyte ATP pools. Proc. Natl. Acad. Sci. USA 86:1662-1666 [1989]). These elevated levels of ATP inhibit both tumor growth and host weight loss in tumor-bearing murine models. The inhibition of tumor growth proceeds by the receptor-mediated and non-receptor-mediated effects of extracellular ATP on the tumor cell membrane, whereas the inhibition of host weight loss in tumor-bearing hosts is the result of ATP-mediated marked slowdown of hepatic gluconeogenesis and reversal of the depletion of visceral energy stores (Rapaport, E. Mechanisms of anticancer activities of adenine nucleotides in tumor-bearing hosts. Ann. N.Y. Acad. Sci. 603:142-150 [1990]).
Administration of ATP by intravenous infusions at a dose of 50 μg/kg min for at least 48 hours yielded a doubling of blood (red blood cell) ATP levels after 24 hours in advanced cancer patients (most of whom were at stage III B or IV non-small cell lung cancer). Hyperuricemia developed only after at least 48 hours of continuous infusions (Haskell, C. M. and Sanchez-Anaya, D. Hyperuricemia as a complication of ATP: preliminary observation of a phase I clinical trial. ASCO Proceedings 12:435A [1993]) and could be easily dealt with by allopurinol. The elevated blood ATP levels declined within several days after termination of the ATP infusions with a return of total blood ATP levels to their basal levels. In advanced cancer patients with cachexia and malnutrition, the basal blood ATP levels were lower than normal but could be elevated to well above a normal level after ATP infusions.
The mechanisms of expansion of organ ATP levels after administration of ATP proceed by both the increased supply of the major purine precursor for salvage ATP synthesis in cells (adenosine) and the interaction of extracellular ATP with membrane P2-purine receptors which signals an enhanced intracellular ATP synthesis. Most of the expansions of total blood (red blood cell) ATP pools occur due to increased supply of purines to the mature erythrocyte in the hepatic sinusoids, where these purine precursors (mostly adenosine) arise from the increases in turnover of hepatic ATP pools (Rapaport, E. and Fontaine, J. Generation of extracellular ATP in blood and its mediated inhibition of host weight loss in tumor-bearing mice. Biochem. Pharmacol. 38:4261-4266 [1989]). A significant increase in red blood cell ATP pools of the magnitude observed in vivo after ATP administration cannot be obtained in vitro (Rapaport, E. and Fontaine, J. Anticancer activities of adenine nucleotides in mice are mediated through expansion of erythrocyte ATP pools. Proc. Natl. Acad. Sci. USA 86:1662-1666 [1989]).
Adenosine 5′-triphosphate (ATP) infusions useful against metastatic refractory cancers are in Phase I of human clinical trials. The two questions which are being answered by these trials are: 1) is it possible to achieve the degree of elevation of red blood cells, and blood plasma compartment pools of ATP after the administration of ATP to patients as was shown extensively in preclinical murine models, and 2) can the elevated ATP levels in the human host produce the spectrum of anticancer activities demonstrated in experimental animals (Rapaport, E. Mechanisms of anticancer activities of adenine nucleotides in tumor-bearing hosts. Ann. N.Y. Acad. Sci. 603:142-150 [1990]).
A variety of in vitro and in vivo studies have demonstrated several anticancer activities of extracellular (blood plasma compartment) pools of ATP as well as elevated hepatic and red blood cell pools of ATP. These activities are a) cytostatic and cytotoxic effects on the tumor; b) anti-cachexia effects and improvement of hepatic and renal functions; c) modulation of tumoral blood flow; d) antianaemia effects; e) antipain activities; f) improvement in motor functions, performance status; g) improvements in oxygen delivery to peripheral sites; h) enhancement of superoxide anion (O2−) production by phagocytic cells and i) significant antithrombotic effects in vivo. All of these anticancer activities observed either in experimental animals or in humans after the administration of ATP have been reviewed recently (Rapaport, E. Anticancer activities of adenine nucleotides in tumor-bearing hosts. Drug Development Research 28:428-431 [1993]).
The administration of ATP to tumor-bearing murine hosts was also shown to markedly inhibit host weight loss in a cachectic tumor model and, as importantly, the administration of ATP or other adenine nucleotides was shown to elevate extracellular, blood plasma compartment steady state levels (pools) of ATP. The inhibition of tumor growth and host weight loss were shown not to exhibit a cause and effect relationship in murine models. The cytolytic activity of extracellular ATP against tumor cells is now being proposed by five different groups as accounting for the activity of certain cytolytic T lymphocytes (Filippini, A., Taffs, R. E. and Sitkovsky, M. V. Extracellular ATP in T-lymphocyte activation: Possible role in effector functions. Proc. Natl. Acad. Sci. USA 87:8267-8271 [1990]; Di Virgilio, F., Pizzo, P., Zanovello, P., Bronte, V. and Collavo, E. Extracellular ATP as a possible mediator of cell-mediated cytotoxicity. Immunol. Today 11:274-277 [1990]; Zheng, L. M., Zychlincky, A., Liu, C. C., Ojcius, D. M. and Young, J. D. Extracellular ATP as a trigger for apoptosis or programmed cell death. J. Cell Biol. 112:279-288 [1991]; Steinberg, T. H. and Di Virgilio, F. Cell-mediated cytotoxicity: ATP as an effector and the role of target cells. Curr. Opinion Immunol. 3:71-75 [1991]; Correale, P., Tagliaferri, P., Procopio, A., Coppola, V., Caraglia, M., Celio, L. and Bianco, A. R. ATP is a lymphokine activated killer (LAK) cell cytotoxic factor against colon cancer cells in vitro. Proc. Am. Assoc. Cancer Res. 33:324 [1992]). These cytolytic T lymphocytes release ATP which is stored in their cellular granules, in response to the target cell interaction with a T cell receptor. The extracellular ATP released in the immediate vicinity of the target tumor cell is proposed to deliver the lethal hit. All of these groups demonstrated tumor cell killing by extracellular ATP in a variety of systems.